Age-related macular degeneration (AMD) is a condition that primary affects adults ages 65 and older. AMD results in the loss of central vision, which is required for performing tasks like reading, driving, and other activities that require the ability to see detail. In some cases, AMD progresses so slowly that people don't notice the changes in their vision over time. In other cases, the disease progresses more rapidly and can lead to a complete loss of central vision. While those with age-related macular degeneration retain their peripheral vision, AMD destroys sharp, central vision and may affect perception of color and contrast.

AMD results from damage to the macula, a small portion of light-receptive tissue at the back of the retina. The retina functions by processing light and converting it to electrical impulses that are sent to the brain via the optic nerve. The macula is the most sensitive part of the retina, and its function is to assist in processing fine details. When the macula is damaged, this causes a gradual loss in the ability to transmit these fine details to the brain which in some cases is difficult to correct with prescription glasses.

Types of AMD

Dry AMD is by far the most common type, affecting about 90% of AMD sufferers. This type of AMD results from a breakdown or thinning of cells in the macula. These cells are called retinal pigment epithelial cells (RPE). The atrophy of RPE cells renders them unable to support the photoreceptor cells that process images and relay them to the brain.

Though it is far less common, wet AMD results in the vast majority of cases of severe AMD-related loss of vision. his type of AMD is caused by disruption in the supply of oxygen to the macula due to retinal thickening and breaking. The body responds by producing new blood vessels to the area, which grow through these retinal breaks and push on the macula. These vessels can leak or bleed into the retinal breaks.

Risk Factors

The primary risk factor for age-related macular degeneration is age. The disease is relatively rare in those under age 60, with an overall chance of developing AMD of about 2%. Adults age 75 and older have a 30% chance of developing the condition. Other factors that may increase the risk of developing AMD include hereditary factors such as family history, race, and gender. Whites are more likely to develop AMD than African Americans, and women are more likely to develop the condition than men. Lifestyle factors like smoking and obesity can also increase the risk of developing AMD.

Symptoms and Diagnosis

Neither form of AMD is painful, and the dry and wet forms of the condition have distinct symptoms. One of the first signs of dry AMD is blurred vision due to damaged light sensing cells. Sometimes this blurry vision will improve with bright light. When damage to these cells becomes severe, people will typically experience a small blind spot in central vision that gradually grows larger.

A typical early symptom of wet AMD is when straight lines begin to appear crooked or distorted. This happens because of the displacement of the macula due to pressure from fluid that is leaked from the newly formed blood vessels. Those with wet AMD may also notice a small blind spot in their central vision.

AMD is detected using a variety of diagnostic tests during an eye exam. These include a visual acuity test that measures distance vision, a dilated eye exam in which the optometrist examines the structures of the eye for damage, and tonometry to measure pressure changes within the eye.

Treatments and AMD Research

Wet AMD can be treated using a variety of approaches. These include laser surgery, photodynamic therapy, and injections. There is no treatment for advanced dry AMD, but results of the Age-Related Eye Disease Study (AREDS) show that a specific formulation of high-dose antioxidants and zinc can slow the progression of the disease and save vision in many patients with the condition.

The National Eye Institute, an arm of the U.S. National Institutes of Health, is conducting a second AREDS study (AREDS2). Other studies underway include investigating whether or not it's possible to transplant healthy retinal cells into a diseased retina, analyzing family history data to better understand hereditary factors in AMD development, and researching the effectiveness of treating wet AMD with anti-inflammatory agents.